Jeannie Yandel talks with University of Washington geology professor Terry Swanson about glacial erratics and how one might be blocking the tunneling machine named Bertha.
Is An Ice Age Boulder Blocking Bertha?
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Flickr Photo/WSDOT
Jeannie Yandel talks with University of Washington geology professor Terry Swanson about glacial erratics and how one might be blocking the tunneling machine named Bertha.